Phase comparison system



' SUPPLY C Dec. 25, 1956 A, M. MacCALLUM ET AL 2,775,712

PHASE COMPARISON SYSTEM Original Filed June 28, 1948 CONVERTER '10 FIG.1.

A.C. PLATE VOLTAGE wl l B 3' w I 9- A.C. UTILIZING MEANS BRANCH A IQ HP- slcNAL CONVERTER INVERTER SIGNAL AM: A A A 4oo- VOLTAGE, A VOLTAGE BsuP SUPPLY v 400 BRANCH B Q g;

@WNAL 6 coNvERTER INVERTER VOLTAGE IN VEN TORS ALAN M. MAC CALLUM CORLESM. PERKINS AL ED BENNETT United States Patent PHASE COMPARISON SYSTEMAlan M. MacCallum, Plainfield, and Corles M. Perkins, Rutherford, N. J.,and Alfred Bennett, Bronx, N. Y.

Original application June 28, 1948 Serial No. 35,606. Divided and thisapplication July 26, 1951, Serial No. 238,984

4 Claims. (Cl. 307-73) This invention relates generally to electricalphase comparison systems and has particular application to those systemsincluding means and methods for matching the phase of a plurality ofdiscretely originating signals. This application is a division ofcopending application Serial No. 35,606, filed June 28, 1948, nowabandoned, and assigned to the same assignee as the present application.

Accordingly, it is one of the objects of the present invention toprovide a novel converter comprising an electron discharge device havinga plurality of control electrodes to which a plurality of input signalsmay be directed for obtaining direct current outputs having a polarityand magnitude dependent upon the phase and amplitude of the inputsignals delivered thereto.

Another object of the present invention is to provide a network forcomparing the phase of a multiplicity of A. C. signals.

Yet another object of the present invention is to provide a phasecomparison network for use with A. C. utilizing means.

Still another object of the present invention is to convert received A.C. signals 'into phase sensing indications for use in guidance systems.I

Still another object of the present invention is to provide, in guidancesystems, means for converting an alternating current signal of a givenphase and amplitude into a direct current signal having a polarity andmagnitude directly proportional to the phase and amplitude of said givenA. C. signal.

Another object of the present invention is to provide a frequency mixerfor alternating current signals having differing frequencies.

Another object of the present invention is to provide a novelalternating current converter.

Yet another object of the present invention is to provide, in craftguidance systems, an alternating current converter which may becooperatively associated with a non-electronic type of direct currentinverter which gives an A. C. voltage output proportional, in phase andamplitudc, to the converter signal input, and which may be used forcontrolling suitable guidance mechanism.

A further object of the present invention is to provide a novelconverter for use in a phase comparison network and wherein a directcurrent voltage is obtained which has a polarity and magnitudedirectionally proportional to the input phase and amplitude of analternating current voltage applied thereto.

Still another object of the present invention is to provide means,apparatus and instrumentalities adapted for attaining the foregoingobjects whether such uses or means have been particularly referred to ornot.

In the drawings,

Figure 1 is a circuit diagram of the novel converter and inverter usedin a preferred embodiment of the invention. 7

And, Figure 2 is a block diagram representation illustrating anembodiment of the present invention and showing the arrangement ofcomponents forming a discrimi- "ice nator system utilizable in theguidance of dirigible craft.

Similar reference characters are used in all the above figures toindicate parts having corresponding functions.

Generally speaking, the hereinafter described invention discloses meansfor obtaining output D. C. signals from an A. C. converter having apolarity and magnitude correlated with the phase and amplitude ofalternating current input signals delivered thereto.

The converter comprises an electron discharge device having a pair ofcontrol grids connected to either side of a center-tapped transformer.The anodes or plates of the converter are phasingly related to the phaseof the input signals placed on the control grids. As a result thereof,an output voltage, having a polarity and magnitude which are related inphase and amplitude to the input signals, is taken from the cathoderesistors of the electron discharge device. The D. C. voltage thusderived from the converter is then fed to a non-electronic type ofinverter which, in turn, converts the D. C. signals to correlatedalternating current signals.

By feeding the output of the inverter to a comparison circuit whichcircuit may have a reference generating means included therein, acomparison may be etfectuated between a reference signal included in thecircuit and the input signal from the inverter. This comparison voltagemay be fed to associated A. C. utilization means.

Further, it may be desirable that a second A. C. signal derived from adiscrete source, such as a second transmitter or generator of varyingfrequency, be converted in like manner from an A. C. to a D. C. signaland be combined or mixed with the first signal. This combination ofsignals having different frequencies, and/ or phase, as derived in theaforesaid manner, may be suitably combined so as to control mechanismused in the guidance of dirigible craft, for example, an automaticpilot.

Referring now to the drawings, in Figure 1 a converter 10 is used forreducing an input A. C. voltage of varying amplitude and phase to anoutput D. C. voltage coincidently varying in magnitude and polarity asits A. C. input. Coupled t-o converter 10 is inverter 11 which isutilized to derive an A. C. signal from the D. C. signal obtained fromconverter 10.

Converter 10 comprises a pair of electron discharge devices 23, 23having anodes 24 and 24 to which a suitable A. C. anode voltage isconnected. A centertapped secondary winding 25 of transformer 30 is usedto couple an A. C. signal derived from primary winding 26 of transformer30 from a source of A. C. signals 27. Secondary winding 25 has its ends28 and 29 connected to control electrodes 31 and 32. Cathodes 33 and 34of electron discharge devices 23 and 23 are connected in series withcathode resistors 35 and 36 to ground. It is thus seen that controlelectrodes or grids 31, 32 of electron discharge devices or vacuum tubes23 and 23 are connected in push-pull arrangement; that is, they arearranged to have a phase difference between them by means of inputtransformer 30. It is also seen that cathodes 33, 34 of the tubes areconnected to the plate return through cathode resistors 35 and 36 havinga suitable value for producing the necessary cathode potential foroperation of the tubes. Anodes 24 and 24' are connected together to theA. C. plate voltage, which is of the same phaseas the signal inputapplied to the control electrode or 180 from the signal input appliedthereto.

Substantially the inverter operates so that with no signal applied totransformer 30, plate current will flow through tubes 23 and 23 at thepositive half-cycle of the anode voltage impressed thereupon. As aresult thereof, current will flow through cathode resistors 35 and 36 toproduce a pulsating D. C. voltage across output terminals 37, 38. Sincecathodes 33 and 34 will o .2 vary in potential together, there resultsno net potential across output terminals 37 and 38.

However, when an input signal is applied to primary winding 26 oftransformer 30 in phase, or 180 out of phase, with the voltage appliedto anodes 24 and 24', two voltages appear on each of control electrodes31, 32, each differing by a phase of 180 due to the induced voltagesplaced across secondary winding 25 of transformer 30. Thus, it is seenthat when the voltage appearing on grid 31 is in phase with the anodevoltage, the voltage appearing on the other grid 32 will be 180 out ofthe phase with the anode voltage.

Thus tube 23, in which the control electrode signal is in phase with theplate voltage, necessarily will draw more plate current. As a resultthereof, a greater voltage will appear across cathode resistor 35commensurate with the amount of flow of current therethrough. Tube 23,which has a grid voltage out of phase with the voltage impressed onplate 24 must, therefore, draw less plate current through its associatedresistor 36 and the voltage drop diminishes with the lesser amount ofcurrent flowing therethrough. A resultant potential, therefore, willappear across output terminals 37 and 38 proportional to the differencein plate currents flowing through tubes 23 and 23 and proportional tothe ma nitude of the input A. C. signal.

It is seen, therefore, that a reversal in phase of the input signal totransformer 30 will reverse the phase condition of the voltagesimpressed on the control grids 31, 32 so as to change the amount of flowof current through resistors 35, 36 associated with cathodes 33 and 34.A greater flow of current will oppositely take place therethrough andthus the polarity of the voltage appearing across output terminals 37and 38 will also change.

In this manner, converter 10 will accept an A. C. signal having avariable amplitude and phase and will produce as its output acorrelatively average direct current voltage having a magnitude andpolarity directly correlated with the amplitude and phase of the inputsignal.

The average D. C. signal obtained from converter 10 is next directed toinverter 11 as by means of conductors 60 and 61. Inverter 11, more fullydescribed in U. S. Serial No. 700,234, comprises two cores 40 and 41provided with primary and secondary windings thereon. The primarywinding is split into two pairs of windings 42, 43 and 44, 45 which areconnected together in series aiding relation. The free end of winding 42is connected with one side of an A. C. source 80 and the free end ofwinding 45 is connected with the other side of the source.

The secondary winding is split into two pairs of windings 46, 47 and48,. Windings 46 and 47 are connected in series aiding relation on core40 and wind ings 48 and 49 are connected in series aiding relation oncore 41; the first set of windings 46, 47, however, is connected inseries opposed relation with the second set of windings 48, 49. The freeends of windings 46 and 49 constitute the output taps for an A. C.signal developed therein.

The center leg of each of core 40 and 41 is provided with controlwindings 50 and 51 which are connected in series aiding relation witheach other and their free ends are connected to the D. C. signal outputfrom converter 10. Other control windings 52 and 53 are provided on thecenter legs of the cores and are connected with each other in seriesopposed relation and are fed by D. C. current from a suitable source 81.

With no D. C. control signal in windings 50 and 51, the device isbalanced and no signal appears at the secondary output. While flux flowsin core 40 due to A. C. current in windings 42 and 43 and in core 41 dueto A. C. current in windings 44 and 45, the output of the secondarywindings is zero because the current induced in windings 46 and 47 ofcore 40 is equal and opposite to the current induced in secondarywindings 48 and 49 of core 41. Since the direct current in both controlcoils 52 and 53 is of the same value the balance of the system is notdisturbed.

Once D. C. current from converter 10 flows in control coils 50 and 51,however, the flux of coil 50 will add with the flux of coil 52 of core40 saturating the latter core, thereby making it a poor transformerwhile the flux of coil 51 will oppose the flux of coil 53 of core 41making the latter a better transformer so that the device becomesunbalanced and an A. C. current will flow at the secondary output. Thedirection that the A. C. current will flow in the secondary isdetermined by the direction of the D. C. signal current in controlwindings 50 and 51.

Since the output derived from inverter 1=1 is an A. C. voltage having aphase and amplitude directly correlated to the amplitude and phase ofincoming A. C. signals received by inverter .10, it is possible to feeda multiplicity of A. C. signals to inverter 10 which may have a phaseand amplitude independent of each other and to combine or mix thesesignals in inverter 11 to obtain a combination signal having a phase andamplitude which is a function of the plural inputs.

Such a case is found where it is desired to obtain a signal for theguidance of dirigible craft, as in the automatic piloting of craft,where signals representing a displacement from a reference and rate ofdisplacement from that reference are mixed to give a combination signalfor use in guiding the craft. In the usual case, these signals are soarranged that they are supplied from a common voltage source and aremade to agree in phase so as to be mixed directly.

However, many times it is desirable to mix a plurality of signals whosephases do not agree, and perhaps whose frequencies may not be the sameor of the same nominal value but having a value which varies about someother signal. By the hereindescribed inverter, it is possible to combinea plurality of signals to give a single voltage having a variable phaseand amplitude regardless of the input frequency and phase angles.

Referring now to Figure 2, signal a, is a reversible phase, variableamplitude signal having a definite basic frequency, for example, 25cycles per second. Signal 0 is a signal similar in character to that ofsignal a but having a difierent basic frequency; for example, 60 cyclesper second. Assume, for example, that for the guidance of a dirigi'blecraft an output is desired which is a combination of these two signalsbut which has a frequency of 400 cycles per second. Signal a is fed intoconverter :10 of branch A as described above. The resulting output fromconverter 10 is a D. C. voltage which varies in polarity and magnitudein accordance with the phase and amplitude of input signal a. Thisoutput D. C. voltage is then introduced into inverter 11 where it isconverted into an A. C. voltage having a variable phase and magnitudewith respect to a voltage b utilized as a reference voltage. Thefrequency of the A. C. output signal, however, is at the frequency ofvoltage b which, in this case, is 400 cycles per second.

In a similar fashion, a signal c may be conducted through parallelbranch B, first being changed in converter 20 to a D. C. voltage whichvaries in polarity and magnitude in accordance with the phase andamplitude of signal 0. The D. C. voltage is next changed in inverter 22to an alternating current voltage having a variable phase and amplitudewith respect to voltage a, but also having the frequency of voltage b.The two outputs, one from inverter a and the other from inverter c, maythen be combined directly for utilization as desired since they are nowof the same frequency and same phase.

It is seen then, that the device described above may be utilized toperform a mulitude of different functions, viz: to combine signals ofdifferent phases having the same frequency; or as a frequency changer,per se.

Since various changes and modifications to the form and relativearrangement of the parts described herein may appear to those skilled inthe art, it is not intended that the scope of the invention berestricted to the recitations made herein, but rather is to be obtainedfrom a reading of the specification in conjunction with the hereappended claims.

What is claimed is:

1. A network for combining signals of diflerent frequencies to provide asummation signal of one frequency, comprising a pair of convertersadapted to receive alternating current signals of different frequenciesand producing D. C. voltages at their outputs having polaritiesdetermined by the phases of the signals, an inverter connected to eachof said converters and energized by an alternating current source ofsaid one frequency and controlled by the 'D. C. voltage from theassociated converter, said inverters providing alternating currentvoltages having said one frequency and having a phase determined by thepolarity of the D. C. voltage, and means for combining said alternatingvoltages from said inverters.

2. A signal chain for a control system, comprising a plurality ofconverters adapted to receive alternating current signals of differentfrequencies and each converter being energized by an alternating currentsource of the same frequency as the associated signal, each of saidconverters producing a D. C. voltage at its output having a polaritydetermined by the relative phase of the alternating current source andsignal, an inverter connected to each of said converters and energizedby a common alternating current source and controlled by the D. C.voltage from the associated converter, said inverters providingalternating current voltages of the same frequency as the associatedenergizing current source and the phase of said signals relative to thephase of said associated source being determined by the polarity of theD. C. voltages, and means for adding said alternating current voltagesfrom said inverters algebraically.

3. \A network for the summation of control signals of differentfrequencies comprising a first converter for receiving a firstalternating current signal of one frequency and adapted to be energizedby an alternating current source having the same frequency as the firstsignal, a second converter for receiving a second signal of a differentfrequency and adapted to be energized by an alter nating current sourceof the same frequency as the second signal, each of said convertersproducing D. C. voltages at their outputs having polarities determinedby the phase of the corresponding signal, an inverter connected to eachof said converters and energized by a common alternating current sourcefor receiving the output of the associated converter and providing anoutput alternating voltage having a phase determined by the polarity ofthe D. C. volt age and a frequency corresponding to the commonalternating current source, and means connecting the outputs of saidconverters in series with one another and providing the algebraic sum ofthe output alt-erntaing voltages.

4. A network for providing a signal corresponding to a summation ofsignals having different frequencies and having reversible phases andvariable amplitudes, comprising a plurality of converters, each adaptedto receive an alternating current signal of different frequency and eachincluding a transformer and a pair of electron tubes, said transformerhaving a primary winding for receiving the signal and a center tappedsecondary winding on which the signal is coupled, said tubes havinganodes, control grids and cathodes, means exciting said anodes from analternating current of the same frequency as the signal received on saidprimary Winding, means connecting said control grids to the oppositeends of said secondary Winding, whereby the signal and anode voltagesare in phase in one tube and in phase opposition in the other tubedepending upon the phase of the signal, and impedances connecting saidcathodes and the center tap of said secondary winding whereby thedifierential direct current voltage across said impedances correspondsin magnitude and polarity to the amplitude and phase of said signal, aninverter connected to each converter, said inverters each including apair of transformers having cores normally saturated alike and havingprimary, secondary and control windings thereon, means energizing saidlast primary windings from a source of alternating current of onefrequency, said last secondary windings being normally balanced againsteach other, and means supplying said control windings with saiddifferential direct current voltage whereby said direct current voltagediiferentially saturates said cores to unbalance said secondary windingsto develop an alternating current output having said one frequency andbeing modulated in accordance with said direct current voltage, andmeans connecting the secondary windings of said inverters together toprovide a summation of said outputs.

References Cited in the file of this patent UNITED STATES PATENTS1,705,993 Oswald Mar. 19, 1929 2,411,916 Woodyard Dec. 3, 1946 2,429,216Bellman et al. Oct. 21, 1947 2,453,624 Glass Nov. 9, 1948 2,467,347Truckses Apr. 12, 1949 2,561,329 Ahlen July 24, 1951 2,565,621 OlsonAug. 28, 1951 2,640,939 Staschoven et a1. June 2, 1953 2,697,808MacNichol et a1 Dec. 21, 1954

